The relationship of Campylobacter pyloridis to human gastroduodenal disease is not understood. Numerous studies hypothesized that this species is the etiological agent but rigorous proof has not been forthcoming. This is partly because animal models are not available and epidemiological studies have been hindered by the lack of a system for serotyping the strains. The proposal has as its priority the development of serotyping schemes based on both lipopolysaccharide (O) antigens and thermolabile antigens. The production of a set of monoclonal antibodies to enhance the specificity of the serotyping is also proposed. The specificity of the systems and their applicability for routine serotyping in reference laboratories are to be assessed in practical situations and by bacterial chromosomal restriction endonuclease DNA digest analysis. The serotyping systems will be used to support ongoing investigations that have been designed to examine patients and normals prospectively and also to provide serotyping to others involved in studying the epidemiology of gastroduodenal disease. Studies at the molecular level are to be undertaken to determine the nature of the lipopolysaccharides in C. pyloridis and to examine the proteins of the outer membrane and flagella to identify serotypic markers and common antigens. The common antigens will be evaluated as potential candidates for vaccine productions and for developing improved rapid diagnostic tests. Because of its known importance the urease enzyme will be given special attention in these studies. The longer term objective is to conduct epidemiological studies to trace the sources and routes of transmission of C. pyloridis and obtain convincing evidence to delineate the role of the species in diseases of the stomach and duodenum.